Ignore .env
Ignore .env

We have instructions in the README advising devs to create a .env
file for local development. If they're not careful, this file
could be committed to GitHub and they'd compromise their access
token. We should ignore it to ensure that can't happen.

alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs